Micromechanical sensors are used in various technical applications, for example, as motion sensors for detecting the instantaneous acceleration or yaw rate. These motion sensors are frequently based on microelectromechanical systems (MEMS) which may be read out capacitively, in which the motion of a seismic mass is converted with the aid of a suitable electrode system into a measurable capacitance change. Corresponding electrodes may also be used for the capacitive excitation of the motion of the seismic mass.
The sensitivity of microelectromechanical sensors is a function of various parameters, which may be controlled to varying extents in the manufacturing method. Scattering in the manufacturing process thus frequently results in deviations in the desired geometry of a sensor structure, whereby the response behavior of the sensor may be negatively influenced. For example, the process-related variation in the edge loss or thickness variations of the produced layers come into consideration as error sources. The latter determine the height and the spacing of the produced structures. Thus, for example, the measuring sensitivity of a capacitive sensor is decisively a function of the spacing of the sensor electrodes, which, in the case of a z-acceleration sensor designed as a rocker (out-of-plane sensor element), is typically set with the aid of a spacer layer, which is produced as a sacrificial layer and removed again after the sensor body is finished. Since the spacer layer thickness may only be established with inadequate precision in the manufacturing process, the spacing of the two measuring electrodes of the sensor varies, and therefore also its measuring sensitivity from sensor to sensor. Because of these sensitivity variations, complex mechanical compensation methods must be performed in the respective sensors, the typical accelerations having to be applied to each sensor and the internal amplification pathways having to be adapted on the basis of the particular sensor response.
Alternatively, all process controls, such as the thickness of the individual layers or the edge loss (the difference between the width of a structure provided in the layout and the structure width actually achieved after the processing), must be known as much as possible, so that their effects on the functional parameters may be compensated for by computer.
The prior test methods do not allow certain processing parameters for the sensitivity compensation of a z-acceleration sensor, in particular the sacrificial layer thickness, to be determined with sufficient precision.
It is therefore an object of the present invention to provide a test structure which may be integrated into the sensor core, and which allows a precise determination of the thickness of a spacer layer.